1. Field of the Invention
The present invention relates to a method and device for opening a spout attachment portion formed at the top end of a bag and more particularly to a method and device for opening a spout attachment portion formed by cutting off a corner that is at the top edge and one side edge of a bag. The present invention is applicable to, for example, an apparatus that manufactures bags that have spouts.
2. Description of the Related Art
Patent Reference 1: Japanese Patent Application Laid-Open (Kokai) No. 2014-80013
Patent Reference 2: Japanese Patent No. 5,459,114
Patent Reference 1 discloses how a bag that is equipped with a spout is manufactured. In this art, a pair of left and right grippers clamp or hold both sides of a spout attachment portion of each one of bags in which the spout attachment portion has been formed by cutting off a corner of the top edge and one side edge of the bag, the bag is hung down so that the spout attachment portion is substantially horizontal, and the thus hung down bags are intermittently conveyed along a specific conveyance path; and at various stop positions along the conveyance path, an opening step, in which the spout attachment portion is opened, a spout insertion and temporary sealing step, in which a spout is inserted into the opened spout attachment portion and then temporarily sealed, and a final sealing step, in which the spout is finally sealed to the spout attachment portion, are performed. The bag disclosed in Patent Reference 1 is one that is entirely sealed including the top edge, except for the spout attachment portion. Patent Reference 1 describes that the bag is filled with its contents through the spout attachment portion, and this filling is done after opening up the spout attachment portion and before attaching the spout to the spout attachment portion.
The bag disclosed in Patent Reference 2 is one in which a spout attachment portion is formed by cutting off a corner that is at the top edge and one side edge of a bag, but neither the spout attachment portion nor the top edge is sealed. Patent Reference 2 discloses that after a spout is attached to the spout attachment portion, the top edge (an opening used for filling) of the bag is opened up, and then the bag is filled with a liquid through this opening in the top edge.
In a bag that has a corner-cut spout attachment portion and a sealed top edge, when opening the spout attachment portion (see Patent Reference 1), it is preferable that the bag surfaces near the spout attachment portion (more specifically, the films on both sides of the bag) be suction-held by a pair of opening suction cups, the suctions cups be then retracted to open up the spout attachment portion, and then using a gas blowing member (see Japanese Patent Application Laid-Open (Kokai) No. 2002-128025, for example) a gas is blown into the bag through the opened spout attachment portion, thus inflating the bag. These steps are taken because by way of inflating the bag, the opening shape of the spout attachment portion of a bag is allowed to be kept stable (without returning to the original, closed shape) even after the opening suction cups that suction-held the bag surfaces are separated from the bag surfaces, and the bag can be conveyed in this opened state to the next step.
On the other hand, for the bag disclosed in Patent Reference 2 (a bag in which the spout attachment portion and the top edge are not sealed), it is difficult to inflate the bag sufficiently even when a gas blowing member is used to keep blowing gas into the bag through the opened spout attachment portion. This aspect will be described with reference to FIG. 10.
As shown in FIG. 10, a bag 1 has a corner-cut spout attachment portion 2; and side edges 3 and 4 and a bottom edge 5 are sealed, and the spout attachment portion 2 and the top edge 6 are not sealed. As discussed in Patent Reference 1, left and right pairs of grippers 7 clamp or hold the side edge 3 and the top edge 6 on both sides of the spout attachment portion 2, and the bag 1 is allowed to be hung down so that the spout attachment portion 2 is made horizontal. The grippers 7 are the same as the left and right pairs of grippers disclosed in Patent Reference 1 in that they are moved intermittently along a specific conveyance path and intermittently convey the clamped bag 1 along a specific conveyance path.
In FIG. 10, a pair of opening suction cups 8 (only one opening suction cup 8 is shown) suction-hold the films on both sides of the bag 1 at a position slightly under the spout attachment portion 2, and then they are retracted (or moved away from each other), thus opening the spout attachment portion 2. As is commonly known, when the opening suction cups 8 are refracted, the grippers 7 are moved closer to each other so as not to hinder the opening of the spout attachment portion 2. A gas blowing member 9 disposed above the bag 1 is moved up and down; and when the spout attachment portion 2 is opened, the gas blowing member 9 is descended, the lower end of its head 9a is brought into the opening of the spout attachment portion 2 so as to block off the spout attachment portion 2 substantially completely, and then a pressurized gas is blown into the bag 1. The reference numeral 11 is a gas channel formed in the gas blowing member 9, one end of this gas channel opens to the lower end of the head 9a (the pressurized gas blow hole), and the other end of which is connected to a pressurized gas supply 12. The reference numeral 13 is an elevator member linked to the gas blowing member 9, and it is moved up and down by an elevator drive source (not shown).
Since the bag 1 is not sealed at the top edge 6, as seen from FIG. 10, when pressurized gas is blown down from the gas blowing member 9, the unclosed top edge 6 becomes an escape path for the pressurized gas, the pressurized gas freely flows out of the bag (see the white arrows in FIG. 10), the gas does not extend throughout the interior of the bag 1, and the center region 14 of the bag 1 under the spout attachment portion 2 (the region surrounded by the two-dot chain line) is particularly difficult to inflate. If this region 14 does not inflate completely, the region 14, after the opening suction cups 8 are separated from the bag surface, will return to its original closed (or flat) state under the restoration force of the films of the bag 1, which results in a narrowing, deformation, etc., of the opening of the spout attachment portion 2, which means that the opening shape of the spout attachment portion 2 tends to be unstable. In particular, when the bag is clamped or held by grippers 7 at an angle, as in this shown example, the above-described restoration force is not exerted symmetrically on both ends of the spout attachment portion 2, and the opening shape of the spout attachment portion 2 tends to be even less stable.